The invention relates generally to methods of repairing worn wear parts and, more particularly, to the refurbishment of worn flight bars used in chain scraper conveyors to transport coal in longwall mining, for example. It is common in longwall mining to transport the cut coal from the shearing face of the seam by way of a so-called armored face conveyor or "AFC" in order to move high tonnages of coal from the area of the mining machine to a main conveyor belt and, thence, out of the mine. A typical AFC is made up of a number of interconnected line pans having profiled side channel guides, commonly referred to as "sigma sections", so named due to the close similarity of their cross-sectional configuration with that of the capital Greek letter. A plurality of elongated flight bars, interconnected by one or two continuous chains, slide along the line pans to move the cut coal therein. The ends of the flight bars are specially contoured to slidably fit within the contoured sigma sections of the line pans and are guided with minimum friction therein, while wedging of material is also minimized. The flight bars are slidably dragged along the line pan by the attached endless chains which, in turn, are driven by powerful motors.
As can be appreciated, there is a great deal of sliding contact between the profiled ends of the flight bars and the similarly contoured and closely fitting sigma sections of the line pans. In order to minimize wear and damage to the more expensive line pan, the sigma sections generally are hardened to a higher degree than the profiled flight bar ends. Thus, after a period of time, the softer end portions of the flight bars become worn down to a degree that excessive clearances develop between the flight bar end portions and the sigma sections and the required guidance provided by the sigma sections is no longer present. When this condition develops, the worn flight bars shift and misalign which can cause serious line breakage and equipment shut-down if the problem is not corrected.
Heretofore, it has been common practice in the coal mining industry to remove and scrap the worn flight bars and replace them with flight bars in a newly manufactured condition. Needless to say, this is an expensive practice which has received some considerable attention in the past, but has yet to be rectified until the present invention.
As stated, prior attempts to repair worn flight bars have not proved entirely successful. One such repair method proposed to build-up or reconstruct the worn tips by hardforming, that is, by direct weld deposition on the worn areas of the flight bar. If the amount of deposited weld material becomes too great in certain areas, it has been found that the hardness of the surface coating will vary, which proves troublesome due to differential wearing. It is also very expensive and difficult to duplicate the complex surface profile geometry of the original flight bar tip by welding or hardforming. When the original tip profile is not duplicated to a substantial degree, the repaired flight bar will cause objectionable increased wear or jamming in the profiled sigma sections of the line pans. Hence, the desired smooth running chain scraper operation will not be realized.
Prior attempts to repair worn flight bars have also utilized a method in which the worn tips were cut off in a straight cut and then a flat faced, bar shaped tip was welded thereon. The welds along interface between the old flight bar and replacement tips were, typically, linearly extending welds, running in a plane co-extensive with the conveying direction. It was found that the forces occurring between the flight bar and the welded-on tips caused high stress areas in the welds and caused the tips to fracture and break off in subsequent service. In addition, the profiles of the endpiece inserts had to be finally shaped by welding deposition to match the original tip profile and this feature proved to be both costly and unsatisfactory due to the inability to consistently reproduce the original tip profile.
The present invention solves the problems heretofore encountered by providing a method of repairing worn flight bars in an economical manner which produces refurbished flight bars having substantially the same tip profiles as newly manufactured flight bars. In addition, the present invention provides a repair method for producing refurbished flight bars having end pieces that will better withstand mining conditions so as to increase the life of the repaired flight bar. Still further, the present invention contemplates a method of repairing flight bars which provides a welding plane configuration which better distributes the loading forces imposed on the flight bar during operation so as to minimize weld fracture problems. In addition, the present invention provides a method of repairing flight bars in a fast and economical manner which includes the use of shaped surfaces on the flight bar and replacement endpieces which fit together in a self-aligning manner for ease in welding, while also assuring reproducible dimensional tolerance control.